Acute oak decline is an emerging disease of oak trees (trees in the Quercus genus) which was first observed in the UK late in the 20th century. It can kill oak trees within four to six years of the onset of symptoms.

The disease is found mostly on mature oak trees, but younger trees can also be affected. It is caused by multiple agents, especially bacteria, and thousands of trees are affected. For infection to occur, it is likely the trees need to be weakened (predisposed) by certain factors, especially environmental factors. For more information, see Acute oak decline – Forest Research.

Ash dieback is a highly destructive disease of ash trees (Fraxinus species), especially the United Kingdom’s native ash species, common ash (Fraxinus excelsior). It is caused by a fungus named Hymenoscyphus fraxineus (H. fraxineus), which is of eastern Asian origin. For more information, see Ash dieback (Hymenoscyphus fraxineus) – Forest Research.

The process by which reactive nitrogen compounds, emitted into the atmosphere from various sources (including aeroplanes, cars, and certain factories), are deposited onto the Earth’s surface. This deposition can occur through both wet (e.g., rain, snow) and dry (e.g., gaseous absorption, particle settling) processes. 

A category of trees that have wide, flat leaves rather than needle-like leaves. These trees are usually deciduous and lose their leaves in winter.

Conifers, or softwood trees, are cone-bearing and usually evergreen trees. They are a distinct group of trees that are economically significant due to their ability to grow quickly even on poor soils and in harsh climates. These trees yield timber that is highly suitable for industrial use, which has led to their widespread planting and management across many countries. Examples of conifer trees found in the UK include Scots pine, Douglas fir, and Norway spruce. 

Dothistroma needle blight (DNB) is an economically important disease of conifer trees (trees with cones and needles), and particularly pines (trees in the Pinus genus). It is caused by the fungus Dothistroma septosporum. It causes premature needle defoliation, resulting in loss of timber yield and, in severe cases, tree death. For more information, please see Dothistroma needle blight (Dothistroma septosporum).

An organism or agent that can cause disease. Pathogens include viruses, bacteria, fungi, and protists. They can infect a wide range of hosts, including plants and animals.

Phytophthora species are highly aggressive tree pathogens causing root rots and foliar and fruit diseases. Aerial Phytophthoras are rain dispersed and can cause foliar and shoot blight and stem and branch cankers. Root rotting species tend to be transmitted in soil and river water and on animal and human vectors and cause feeder root rot and stem collar necrosis. Several Phytophthora species are considered to be involved in the oak decline (for both Quercus robur and Q. petraea) that is reported as widespread across Europe. A number of studies have shown that decline is accelerated or exacerbated when Phytophthoras are present. For more information, see Phytophthoras – Forest Research.